JP2009060098A - Semiconductor device and method for manufacturing semiconductor device - Google Patents

Abstract

Provided are a ZnO-based semiconductor element that can be easily made p-type and does not impair light emission characteristics, and a method for manufacturing the semiconductor element.
A semiconductor layer 2 mainly composed of Mg _x Zn _1-x O (0 ≦ x <1) is provided, and the concentration of manganese (Mn) as an impurity contained in the semiconductor layer 2 is 1 × 10 ¹⁶ cm. ^-3 or less.
[Selection] Figure 1

Description

  The present invention relates to a zinc oxide based semiconductor element, and more particularly to a semiconductor element in which acceptor doping is performed and a method for manufacturing the semiconductor element.

  A zinc oxide (ZnO) based semiconductor has a large binding energy of excitons (60 meV) which is a combined body of holes and electrons. Therefore, excitons can exist stably even at room temperature, and photons can be emitted with high efficiency and excellent monochromaticity. For this reason, ZnO-based semiconductors are being applied to light emitting diodes (LEDs), high-speed electronic devices, surface acoustic wave devices, and the like that are used as light sources for illumination and backlights. Here, “ZnO-based” is a mixed crystal material based on ZnO, in which a part of Zn (zinc) is replaced with a group IIA or IIB, and a part of O (oxygen) is a group VIB. Includes replacements or combinations of both.

However, when a ZnO-based semiconductor containing, for example, Mg _x Zn _1-x O (0 ≦ x <1) containing a p-type impurity is used as a p-type semiconductor, activation of an acceptor dopant doped in the ZnO-based semiconductor is performed. There is a problem that it is difficult to obtain a p-type ZnO-based semiconductor. Advances in technology have made it possible to obtain p-type ZnO-based semiconductors, and light emission has been confirmed. However, there are limitations such as the need to use a special substrate called ScAlMgO _4. (For example, see Non-Patent Documents 1 and 2.) Therefore, it is industrially desired to realize a p-type ZnO-based semiconductor film formed on a ZnO substrate.
A. Tsukazaki, et al., “Japanese Journal of Applied Physics vol.44”, 2005, p. 643 A. Tsukazaki, et al., “Nature Materials 4”, 2005, p. 42

  However, even when a ZnO substrate is used, a p-type ZnO-based semiconductor cannot be easily obtained. When there is a capture center that captures free carriers generated in the ZnO-based semiconductor, the capture center inhibits the ZnO-based semiconductor from becoming p-type. In general, transition metals are often trapping centers in semiconductors. The inventors have found that manganese (Mn), which is often used for the purpose of hardening a metal material, is often taken into ZnO. That is, when the number of Mn atoms in the ZnO-based semiconductor is large, there is a problem that it is difficult to make the ZnO-based semiconductor p-type. Furthermore, there are adverse effects on the light emission characteristics and carrier transport characteristics when a ZnO-based semiconductor is used as the light emitting layer.

  In view of the above problems, an object of the present invention is to provide a ZnO-based semiconductor element that can be easily made p-type and does not impair the light emission characteristics, and a method for manufacturing the same.

According to one embodiment of the present invention, a semiconductor layer containing Mg _x Zn _1-x O (0 ≦ x <1) as a main component is provided, and the concentration of manganese as an impurity contained in the semiconductor layer is 1 × 10 ¹⁶ cm. A semiconductor element that is ^-3 or less is provided.

According to another aspect of the present invention, a step of mounting a substrate on a substrate holder made of a material having a Mn concentration of 5000 ppm or less, and Mg _x Zn _1-x O (0 ≦ x) on the substrate mounted on the substrate holder. And a step of crystal-growing a semiconductor layer made of <1).

  According to the present invention, it is possible to provide a ZnO-based semiconductor element that can be easily made p-type and does not impair light emission characteristics, and a method for manufacturing the semiconductor element.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is the material, shape, structure, The layout is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

As shown in FIG. 1, the semiconductor element according to the embodiment of the present invention includes a semiconductor layer 2 mainly composed of Mg _x Zn _1-x O (0 ≦ x <1), and the semiconductor layer 2 has impurities as impurities. The concentration of manganese (Mn) contained is 1 × 10 ¹⁶ cm ⁻³ or less. The semiconductor layer 2 is made of undoped Mg _x Zn _1-x O or Mg _x Zn _1-x O containing n-type impurities or p-type impurities except for unintended impurities.

  The p-type impurity contained in the semiconductor layer 2 is an impurity doped in the semiconductor layer 2, and for example, nitrogen (N), copper (Cu), phosphorus (P), or the like can be used. As the n-type impurity contained in the semiconductor layer 2, for example, a group III semiconductor such as aluminum (Al) or gallium (Ga) can be employed.

The semiconductor layer 2 is disposed on the substrate main surface 111 of the substrate 1. As the substrate 1, for example, Mg _y Zn _1-y O (0 ≦ y <1) can be adopted. A ZnO-based semiconductor has a hexagonal crystal structure called wurzeite, like gallium nitride (GaN). Therefore, the crystal structures of the substrate 1 and the semiconductor layer 2 are hexagonal. Here, the substrate main surface 111 is a c-plane. Therefore, the main surface of the semiconductor layer 2 formed by growing Mg _x Zn _1-x O on the substrate main surface 111 is a c-plane. FIG. 2 shows a hexagonal crystal structure. FIG. 2 is a schematic diagram showing a unit cell having a hexagonal crystal structure.

  As shown in FIG. 2, the hexagonal c-axis (0001) extends in the axial direction of the hexagonal column, and the plane (the top surface of the hexagonal column) having the c-axis as a normal is the c-plane {0001}. . The c-plane shows different properties on the + c-axis side and the −c-axis side and is called a polar plane. In a hexagonal crystal, the polarization direction is along the c-axis.

  In the hexagonal system, the side surfaces of the hexagonal columns are each m-plane {1-100}, and the plane passing through a pair of ridge lines that are not adjacent to each other is the a-plane {11-20}. The m-plane and the a-plane are crystal planes perpendicular to the c-plane and are orthogonal to the polarization direction, and thus are nonpolar planes, that is, nonpolar planes.

  The concentration of Mn and the secondary ion intensity of the semiconductor layer 2 are measured by, for example, secondary ion mass spectrometry (SIMS) using quadrupole mass spectrometry. FIG. 3 shows a configuration example of an apparatus that performs SIMS using quadrupole mass spectrometry. From the solid sample 50 irradiated with the primary ions, substances constituting the solid sample are released into the vacuum by a sputtering phenomenon. The emitted substance passes through a magnetic field, so that only secondary ions of a specific mass pass through the quadrupole analyzer 60 and enter the detector 70 for elemental analysis. In SIMS using quadrupole mass spectrometry, the potential of the sample stage on which the solid sample is placed is normally grounded, so that the primary ion extraction energy becomes the incident energy as it is. For this reason, when high depth resolution is required, analysis can be performed with the acceleration energy of the primary ions as low as possible.

  As already described, when the semiconductor layer 2 contains a large amount of Mn atoms serving as trapping centers for capturing free carriers, the p-type conversion of the semiconductor layer 2 is inhibited. Therefore, by suppressing the number of Mn atoms contained in the semiconductor layer 2, the semiconductor layer 2 can be easily made p-type.

Currently, in order to form a ZnO-based semiconductor film including a Mg _x Zn _1-x O film with high purity, a molecular beam epitaxy (MBE) method is generally employed. Since the MBE method uses an elemental material as a raw material, the purity at the time of the raw material can be increased as compared with a metal organic chemical vapor deposition (MOCVD) method using a compound material.

  FIG. 4 shows an example of a thin film forming apparatus that can be used in the MBE method for forming a semiconductor element according to an embodiment of the present invention. The thin film forming apparatus shown in FIG. 4 includes a heating source 10 for heating the substrate 1, a substrate holder 20 for holding the substrate 1, and a cell 11 and a cell 12 for supplying a raw material for the semiconductor layer 2 formed on the substrate 1. An infrared lamp or the like can be used as the heating source 10.

  In the example shown in FIG. 4, zinc (Zn) is supplied from the cell 11. The cell 12 is a radical generator and is used when the MBE method is applied to crystal growth of a compound containing a gas element such as a ZnO film. The radical generator usually has a structure in which a high-frequency coil 122 surrounds the outer periphery of a discharge tube 121 made of PBN (pyrolytic boron initiator) or quartz, and the high-frequency coil 122 is connected to a high-frequency power source (not shown). In the example shown in FIG. 4, a high frequency voltage (electric field) is applied to oxygen (O) supplied into the cell 12 by the high frequency coil 122 to generate plasma, and plasma particles (O *) are supplied from the cell 12. The

  As the material of the substrate holder 20, inconel, which is a nickel (Ni) -based alloy having excellent heat resistance and oxidation resistance, ceramic, and the like can be generally used. A stainless steel (SUS) material often used for a substrate holder of a crystal growth apparatus corrodes at a high temperature during growth of an oxide crystal such as ZnO, and thus forms a semiconductor element according to an embodiment of the present invention. It cannot be used with the MBE method. There are many types of Inconel, but unlike SUS mainly composed of iron (Fe), Ni is mainly composed of Mn, aluminum (Al), chromium (Cr), Fe, etc., and Ni. Alloy. However, in order to prevent Mn contained in the substrate holder 20 from being mixed into the semiconductor layer 2 during crystal growth and hindering the p-type of the semiconductor layer 2, the Inconel used for the substrate holder 20 as described below is used. Care should be taken with the material.

  5 (a) to 5 (d), after the Inconel plate is heated to 1000 ° C. in the atmosphere to oxidize it until the surface becomes black, the cross section is shown with a scanning electron microscope and an energy dispersive X-ray analyzer. The result observed by combined SEM-EDX is shown. FIGS. 5A to 5D show oxygen (O), Cr, Mn, and Ni elements in the Inconel plate cross section, and the upper side of each drawing is the surface of the Inconel plate. As shown in FIGS. 5A to 5D, oxidized Cr and Mn are present on the surface of the Inconel plate. While Cr oxide is a material that is very difficult to sublimate, Mn oxide is a material that is easily sublimated.

  6A and 6B, a semiconductor layer 2 made of MgZnO is formed on a substrate 1 made of ZnO by using a thin film forming apparatus employing Inconel containing Mn for the substrate holder 20, and this semiconductor layer The example of the result of having measured the elemental density | concentration of 2 and secondary ion intensity | strength by SIMS using quadrupole mass spectrometry is shown. FIG. 6A shows the analysis result when the input power of the heater used as the heating source 10 is 740 W and the temperature of the substrate holder 20 is 1043 ° C. FIG. 6B shows an analysis result when the heater input power is 510 W and the temperature of the substrate holder 20 is 860 ° C. In FIG. 6A and FIG. 6B, the region where the secondary ion intensity of Mg on the right end side of the graph is low is the data of the ZnO substrate. 6A and 6B, Mn is present between the substrate 1 and the semiconductor layer 2 at a high concentration. And the Mn density | concentration in the semiconductor layer 2 is so high that the input electric power of a heater is high and the substrate holder 20 becomes high temperature. In the thin film forming apparatus, the substrate holder 20 exists closest to the substrate 1. For this reason, it is considered that Mn is supplied from the substrate holder 20 to the substrate 1.

  6A and 6B, the Mn concentration during film formation is lower than that at the interface with the substrate 1 because the Mn oxide is not easily sublimated in the state where oxygen is supplied. It is done. In order to remove moisture and the like, the substrate 1 is annealed at a temperature higher than the crystal growth temperature in a vacuum before film formation while being held by the substrate holder 20. Therefore, it is considered that Mn oxide on the surface of the substrate holder 20 is sublimated during the annealing and adheres to the surface of the substrate 1.

  As described above, from FIG. 5 (a) to FIG. 5 (d) and FIG. 6 (a) to FIG. 6 (b), inconel containing Mn is applied to the substrate holder 20 of the thin film forming apparatus shown in FIG. It has been clarified that when the semiconductor layer 2 made of a ZnO-based semiconductor is grown on the substrate 1 by adopting it, Mn is supplied from the substrate holder 20 to the semiconductor layer 2 as an unintended impurity.

In the ZnO film mixed with Mn, carriers are deficient, and the carrier mobility of about 150 cm ² / Vs is usually reduced to about several tens of cm ² / Vs. FIG. 7A and FIG. 7B compare room temperature photoluminescence (PL) integrated intensities of samples in which the semiconductor layers 2 on the ZnO substrate having different Mn impurity concentrations are stacked. The PL integrated intensity here is an integrated intensity at room temperature obtained by integrating the PL intensity in the range of 340 nm to 420 nm. FIG. 7A shows the secondary ion intensity and Al concentration of Mn of a sample with a PL integrated intensity of 1700, and FIG. 7B shows the sample with a PL integrated intensity of 8300. From FIG. 7A and FIG. 7B, it can be seen that the PL integrated intensity increases as the secondary ion intensity of Mn decreases. That is, as the secondary ion intensity of Mn of the semiconductor layer 2 is increased, the light emission characteristics are degraded.

  As described above, the lower the carrier mobility and the light emission characteristics of the ZnO film mixed with a larger amount of Mn, it is indicated that Mn is a free carrier trapping center. Therefore, in order not to deteriorate the light emission characteristics and carrier transport characteristics of undoped, n-type, and p-type ZnO-based semiconductors and to make the ZnO-based semiconductors p-type, it is preferable that the number of Mn contained in the ZnO-based semiconductor is smaller. .

The semiconductor layer 2 made of a ZnO-based semiconductor in which the number of Mn contained is suppressed can be realized by employing a substrate holder 20 made of ceramic such as silicon carbide (SiC). FIG. 8 shows the result of forming the semiconductor element shown in FIG. 1 with a thin film forming apparatus employing SiC on the substrate holder 20 and measuring the secondary ion intensity of the semiconductor layer 2 by SIMS using quadrupole mass spectrometry. An example of As shown in FIG. 8, carbon (C), silicon (Si), and hydrogen (H) are present in the semiconductor element, but the Mn concentration is 1 × 10 ¹⁶ cm ⁻³ or less. Further, the phenomenon that Mn exists at a high concentration between the substrate 1 and the semiconductor layer 2 as in the case of FIGS. 6A and 6B is not observed. That is, by adopting the substrate holder 20 made of SiC, the semiconductor layer 2 can be easily made p-type.

Alternatively, it is possible to realize the semiconductor layer 2 in which the number of contained Mn is suppressed by employing the substrate holder 20 made of Ni which is a factor of heat resistance and oxidation resistance of Inconel. As shown in FIG. 5D, Ni in Inconel is hardly oxidized. In FIG. 9, the semiconductor element shown in FIG. 1 is formed by a thin film forming apparatus employing a substrate holder 20 made of Ni, and the concentration of elements contained in the semiconductor layer 2 is 2 by SIMS using quadrupole mass spectrometry. The example of the result of having measured the next ionic strength is shown. The secondary ion intensity of Mg in FIG. 9 serves as a marker indicating the boundary between the substrate 1 and the semiconductor layer 2. As shown in FIG. 9, the Mn concentration is 1 × 10 ¹⁶ cm ⁻³ or less. Further, the phenomenon that Mn exists at a high concentration between the substrate 1 and the semiconductor layer 2 as in the case of FIGS. 6A and 6B is not observed. For this reason, it is easy to make the semiconductor layer 2 p-type.

In the semiconductor element according to the embodiment of the present invention, the number of Mn atoms contained as unintended impurities in the semiconductor layer 2 is suppressed, and the Mn concentration measured by SIMS using quadrupole mass spectrometry is 1 × 10 ^16. cm ⁻³ or less. That is, since the semiconductor layer 2 has a small amount of Mn serving as a trapping center for capturing free carriers, the semiconductor layer 2 can be easily made p-type by acceptor doping such as nitrogen. And, using an undoped, n-type or p-type semiconductor layer 2 that does not contain Mn, an ultraviolet LED used as a light source for illumination, backlight, etc., a high-speed electronic device using ZnO, a surface acoustic wave device, etc. Is feasible.

  Hereinafter, a method of manufacturing the semiconductor element shown in FIG. 1 using a thin film forming apparatus employing a substrate holder 20 made of Ni will be described. The semiconductor device manufacturing method described below is merely an example, and it is needless to say that the present invention can be realized by various other manufacturing methods including this modification. Here, the Mn concentration of the substrate holder 20 is 3000 ppm or less.

  (A) A substrate 1 having a + c plane as a main surface, for example, made of ZnO is etched with hydrochloric acid, washed with pure water, and then dried with dry nitrogen.

  (B) The substrate 1 is set on the substrate holder 20 and is put into the thin film forming apparatus from the load lock.

(C) The substrate 1 is heated at 900 ° C. for 30 minutes in a vacuum of about 1 × 10 ⁻⁷ Pa.

(D) The substrate temperature is lowered to 800 ° C., NO gas and O ₂ gas are supplied to the cell 12 to generate plasma, and the plasma is supplied together with Mg and Zn adjusted to have a desired composition in advance. A semiconductor layer 2 made of Mg _x Zn _1-x O is grown thereon.

  (E) Thereafter, the semiconductor layer 2 is doped with a p-type impurity. For example, acceptor doping using nitrogen as a p-type impurity is performed.

  In the above description, the example in which the substrate holder 20 made of Ni is employed has been shown. However, the Mn concentration is such that Mn is not mixed into the semiconductor element during crystal growth, for example, 5000 ppm or less, preferably 3000 ppm or less. The substrate holder 20 can be used for manufacturing a semiconductor device according to the embodiment of the present invention. For example, a substrate holder 20 made of SiC or the like can be used.

Acceptor measured by CV measurement of a MOS structure in which MgZnO and a silicon oxide film (SiO ₂ ) are stacked on ZnO when the amount of nitrogen doped MgZnO produced by the method described above is about 5 × 10 ¹⁸ cm ^−3. The value of the concentration difference “N _A −N _D ” between the concentration (N _A ) and the donor concentration (N _D ) is stable at about 6 × 10 ¹⁵ atoms / cm ³ to 2 × 10 ¹⁶ atoms / cm ³ . . On the other hand, in the above MOS structure containing MgZnO manufactured by a thin film forming apparatus employing Inconel containing Mn for the substrate holder 20, the concentration difference “N _A −N _D ” measured by CV measurement is 1 × 10 ¹³ atoms. / Cm ³ to about 1 × 10 ¹⁴ atoms / cm ³ , clearly carrier deficiency occurs, and it is considered that there is a trap center in MgZnO.

As described above, according to the method of manufacturing a semiconductor device according to the embodiment of the present invention, it is not intended by using the thin film forming apparatus that employs the substrate holder 20 that does not contain Mn or has a low Mn concentration. A semiconductor element having the semiconductor layer 2 in which the Mn concentration contained as an impurity is suppressed to 1 × 10 ¹⁶ cm ⁻³ or less can be manufactured. Since the semiconductor layer 2 has a small amount of Mn serving as a capture center for trapping free carriers, it can be easily made p-type by acceptor doping such as nitrogen.

  In the present invention, it is clarified that Mn serving as a capture center that inhibits the p-type ZnO-based semiconductor is supplied from the substrate holder 20 to the semiconductor element, and the substrate holder 20 that does not contain Mn or contains less Mn. It has been shown that a semiconductor device that can be easily made p-type can be realized by adopting it.

  As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operational techniques will be apparent to those skilled in the art. That is, it goes without saying that the present invention includes various embodiments not described herein. Accordingly, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a schematic diagram which shows the structure of the semiconductor element which concerns on embodiment of this invention. It is a schematic diagram for demonstrating a hexagonal crystal structure. It is a schematic diagram which shows the structural example of the apparatus which performs SIMS using quadrupole mass spectrometry. It is a schematic diagram which shows the example of the thin film formation apparatus which manufactures the semiconductor element which concerns on embodiment of this invention. It is a photograph which shows the result of having observed the cross section of the oxidized Inconel board by SEM-EDX. It is a graph which shows the example of the result of having analyzed MgZnO formed using substrate holder 20 containing Mn by SIMS. It is a graph for demonstrating the relationship between the secondary ion intensity | strength of Mn, and PL integral intensity. It is a graph which shows the example of the result of having analyzed MgZnO formed using the substrate holder 20 which consists of SiC by SIMS. It is a graph which shows the example of the result of having analyzed MgZnO formed using the substrate holder 20 which consists of Ni by SIMS.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Semiconductor layer 10 ... Heat source 11, 12 ... Cell 20 ... Substrate holder 50 ... Solid sample 60 ... Quadrupole analyzer 70 ... Detector 111 ... Substrate main surface 121 ... Discharge tube 122 ... High frequency coil

Claims (5)

A semiconductor layer containing Mg _x Zn _1-x O (0 ≦ x <1) as a main component is provided, and the concentration of manganese as an impurity contained in the semiconductor layer is 1 × 10 ¹⁶ cm ⁻³ or less. A semiconductor element.   The semiconductor element according to claim 1, wherein the semiconductor layer contains a p-type impurity. The semiconductor device according to claim 1, further comprising a substrate made of Mg _y Zn _1-y O (0 ≦ y <1), wherein the semiconductor layer is disposed on the substrate.   The semiconductor element according to claim 1, wherein the p-type impurity is nitrogen. Mounting a substrate on a substrate holder made of a material having a manganese concentration of 5000 ppm or less;
Crystal growth of a semiconductor layer made of Mg _x Zn _1-x O (0 ≦ x <1) on the substrate mounted on the substrate holder.